Control valve for variable displacement compressor

ABSTRACT

To provide a control valve for variable displacement compressor employing ON/OFF control, which is capable of taking measures for occurrence of an abnormally high pressure. When a solenoid is OFF, a spring causes a movable core to move a stopper in a direction away from a stationary core and to thereby separate a shaft fixed to the stopper from a valve seat, resulting in opening the control valve. When the solenoid is ON, the movable core is attracted by the stationary core by a stroke longer than that of the shaft, and a spring causes the shaft to seat on the valve seat, resulting in closing the control valve. If a discharge pressure Pd increases to an abnormally high pressure, a differential pressure between the discharge pressure Pd and a pressure Pc in a crankcase pushes the shaft while compressing the spring, so that the discharge pressure Pd flows out to the crankcase. Therefore, the pressure Pc in the crankcase increases and the variable displacement compressor shifts to operate at a minimum discharge capacity, resulting in decreasing the abnormally high pressure.

This application is a continuing application, filed under 35 U.S.C.§111(a), of International Application PCT/JP2005/022845, filed Dec. 13,2005, it being further noted that priority is based upon Japanese PatentApplication No. 2005-007701, filed Jan. 14, 2005.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

This invention relates to a control valve for variable displacementcompressor, and more particularly to a control valve for variabledisplacement compressor, which controls a discharge capacity of avariable displacement compressor of an automotive air conditioningsystem with ON/OFF control.

(2) Description of the Related Art

A compressor that is used in a refrigeration cycle of an automotive airconditioning system is incapable of controlling the rotational speedbecause the compressor uses as a driving source an engine that variesits rotational speed according to a running condition. Therefore, ingeneral, a variable displacement compressor is employed which isdesigned to be capable of changing a discharge capacity of refrigerantin order to secure an adequate cooling capacity, irrespective of therotational speed of the engine.

In general, in a variable displacement compressor, a wobbling plate,which is provided at a variable inclination angle in an airtightcrankcase, is driven and wobbles by rotations of a rotating shaft, thiswobbling plate wobbling makes a piston move back and forth in parallelto the rotating shaft, and this moving piston introduces refrigerant ofa suction chamber into a cylinder where the refrigerant is compressedand is discharged to a discharge chamber. In this operation, bycontrolling the pressure in the crankcase, the inclination angle of thewobbling plate can be changed by a pressure difference received on theboth ends of the piston. This angle change causes the stroke of thepiston to vary, thereby changing the discharge capacity of therefrigerant. A control valve for variable displacement compressor has afunction of changing the pressure in the crankcase.

In general, such a control valve for controlling a discharge capacity ofa variable displacement compressor partly introduces refrigerant of adischarge pressure Pd discharged from a discharge chamber, into anairtight crankcase. By controlling the introducing rate of therefrigerant, a pressure Pc in the crankcase is controlled. For example,a known control valve for variable displacement compressor controls aflow rate of refrigerant to be introduced into a crankcase according toa differential pressure between a discharge pressure Pd in a dischargechamber and a suction pressure Ps in a suction chamber (For example,refer to Japanese Unexamined Patent Publication No. 2001-132650(paragraphs [0043] to [0045], FIG. 4)).

This control valve for variable displacement compressor senses adifferential pressure between the discharge pressure Pd in the dischargechamber and the suction pressure Ps in the suction chamber, and controlsa flow rate of refrigerant of the discharge pressure Pd to be introducedfrom the discharge chamber to the crankcase such that the differentialpressure becomes equal to a differential pressure which is set by asolenoid, resulting in maintaining a fixed discharge capacity ofrefrigerant discharged from the variable displacement compressor.

However, there arises a problem that such a control valve for variabledisplacement compressor has a complex structure and is thereforeexpensive. Another problem is that, in the refrigeration cycle whichuses carbon dioxide whose working pressure is very high as arefrigerant, the variable displacement compressor may be broken when thehigh pressure section in the refrigeration cycle has become an abnormalhigh pressure, in the case where a failure in a control circuit forcontrolling the control valve for variable displacement compressor or apressure sensor for sensing a refrigerant pressure, for example, ahscaused a malfunction of the control valve for variable displacementcompressor.

SUMMARY OF THE INVENTION

This invention has been made in view of the foregoing and intends toprovide a control valve for variable displacement compressor, which hasa simple structure and is capable of preventing the variabledisplacement compressor from being broken due to an abnormally highpressure.

To solve the above problems, there has been provided a control valve forvariable displacement compressor that controls a flow rate ofrefrigerant to be introduced from a discharge chamber to a crankcase ofthe variable displacement compressor with ON/OFF control in order tothereby change a discharge capacity. This control valve comprises: avalve section where a valve element is arranged on a downstream side ofa valve hole for opening and closing the valve hole, into which therefrigerant that is discharged from the discharge chamber is introduced;and a solenoid for opening the valve section in a deenergized state andfor closing the valve section in an energized state. In the solenoid,the valve element that receives a discharge pressure of the refrigerantintroduced from the discharge chamber in a valve-opening direction isheld at a valve-opening position by a first spring imposing an urgingforce in the valve-opening direction in the deenergized state and asecond spring imposing an urging force in a valve-closing diction, andthe valve element is held at a valve-closing position by the secondspring in the energized state.

The above and other objects, features and advantages of the presentinvention will becomes apparent from the following description whentaken in conjunction with the accompanying drawings which illustratepreferred embodiments of the present invention by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a central longitudinal cross-sectional view showing aconstruction of a control valve for variable displacement compressor.

FIG. 2 is a central longitudinal cross-sectional view showing anoperating state of the control valve for variable displacementcompressor when a solenoid is energized.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a preferred embodiment of the present invention will bedescribed with reference to accompanying drawings in detail.

FIG. 1 is a central longitudinal cross-sectional view showing aconstruction of a control valve for variable displacement compressor.FIG. 2 is a central longitudinal cross-sectional view showing anoperating state of the control valve for variable displacementcompressor when a solenoid is energized.

This control valve for variable displacement compressor has a body 10 ofa valve section, as illustrated on the upper side of the figure. Thisbody 10 has a port 11 for receiving a discharge pressure Pd at the uppercentral part of the body 10, and a port 12 through which a controlledpressure Pc is delivered to a crankcase. The port 11 and the port 12communicate with each other inside the body 10. An extending portionfrom the port 11 forms a valve hole, and a portion that is open in aninternal space where the valve hole communicates with the port 12 servesas a valve seat 13.

Under the body 10, a solenoid is disposed. This solenoid has astationary core 14 which is press-fitted to the body 10 from the bottomside of the figure. The lower part of this stationary core 14 is engagedwith a bottomed sleeve 15. The bottomed sleeve 15 is welded to thestationary core 14 and the inside of the bottomed sleeve 15 is held atthe airtight condition. Inside the bottomed sleeve 15, a movable core 16is disposed in an axially movable manner and is urged by a spring 17 ina direction away from the stationary core 14.

In addition, in this solenoid, a shaft 18 is loosely fitted in thestationary core 14 and the movable core 16 in a manner axially extendingtherethrough. The top end of the shaft 18, as viewed in the figure,forms a valve element of the valve section that can be moved to and awayfrom the valve seat 13 of the valve section. To the bottom end of theshaft 18, as viewed in the figure, a stopper 19 is fixed. Between thestopper 19 and the bottom of the bottomed sleeve 15, a spring 20 isdisposed to urge the shaft 18 in a direction toward the valve seat 13.The stopper 19 has an outer diameter larger than the inner diameter ofthe central opening of the movable core 16 where the shaft 18 is looselyfitted. Therefore, while the movable core 16 is separated from thestationary core 14 by the urging force of the spring 17, the stopper 19is brought into contact with the movable core 16 by the urging force ofthe spring 20. While the movable core 16 is attracted by the stationarycore 14, the top end of the shaft 18 (valve element) is seated on thevalve seat 13 by the urging force of the spring 20, so that the stopper19 is separated from the movable core 16.

Then, a coil 21 is disposed around the outer circumference of thebottomed sleeve 15, a yoke 22 and a plate 23, both made of magneticmaterial, are disposed so as to cover the coil 21, and a harness isdrawn to outside through the plate 23 for power supply to the coil 21.When this control valve for variable displacement compressor is mountedin the variable displacement compressor, an O-ring 25 disposed aroundthe body 10 at an upper position than the port 12 prevents a highdischarge pressure Pd from leaking to the medium pressure port 12, andan O-ring 26 disposed around the stationary core 14 seals between themedium pressure port 12 and atmosphere.

The control valve for variable displacement compressor as constructedabove operates as an ON/OFF valve where the valve section is opened andclosed according to the supply of pulse current to the solenoid. Thatis, when the solenoid is deenergized where no current is present in thecoil 21, the movable core 16 is separated from the stationary core 14 bythe spring 17 having a stronger spring force than the spring 20, asshown in FIG. 1. At this time, the movable core 16 pushes the stopper 19downward, as viewed in the figure, against the urging force of thespring 20, and the top end of the shaft 18 (valve element) is separatedfrom the valve seat 13, so that the control valve for variabledisplacement compressor is in open state.

When the solenoid is energized where the coil 21 carries current, themovable core 16 is attracted by the stationary core 14 against theurging force of the spring 17, as shown in FIG. 2. Thereby, the shaft 18is pushed upward by the spring 20, as viewed in the figure, and thevalve element of its top end is seated on the valve seat 13, so that thecontrol valve for variable displacement compressor is in closed state.At this time, a stroke of the movable core 16 moving to be attracted bythe stationary core 14 is set longer than a stroke of the top end of theshaft 18 moving to be seated on the valve seat 13. Therefore, while thecontrol valve for variable displacement compressor is in closed state,the stopper 19 fixed to the shaft 18 is separated from the movable core16.

As described above, this control valve for variable displacementcompressor operates by ON/OFF pulse current supplied to the coil 21.When the solenoid is deenergized, the shaft 18 moves to a position wherethe spring 17 is balanced with the spring 20, so that the control valveis in open state. When the solenoid is energized, the control valve isin closed state by the urging force of the spring 20. A flow rate ofrefrigerant to be supplied to the crankcase is controlled by changing aduty cycle of pulse current.

Next explanation is about how the control valve for variabledisplacement compressor operates under the abnormal condition due tosome trouble in a control device controlling the control valve forvariable displacement compressor or a sensor connected to the controldevice.

If the trouble causes the solenoid to keep the OFF state, the controlvalve for variable displacement compressor is held in the open state. Inthis case, the variable displacement compressor operates at a minimumdischarge capacity, and therefore the pressure of the refrigerationcycle does not abnormally increase.

If the trouble causes the solenoid to keep the ON state, on thecontrary, the control valve for variable displacement compressor is heldin the closed state. Therefore, the continuous operation of the variabledisplacement compressor at a maximum discharge capacity makes pressurehigh abnormally at a high pressure section in the refrigeration cycle.At this time, in the control valve for variable displacement compressor,the port 11 receives a high discharge pressure Pd while the port 12 hasa medium pressure Pc. Since the port 12 communicates with the inside ofthe bottomed sleeve 15 with the movable core 16 contained therein,through a clearance between the stationary core 14 and the shaft 18, thepressure in the bottomed sleeve 15 is equal to the pressure Pc. That is,the shaft 18 receives the discharge pressure Pd in the valve-openingdirection at its top end serving as the valve element, and also receivesthe load of the spring 20 and the pressure Pc in the valve-closingdirection.

As a result of the variable displacement compressor operating at themaximum discharge capacity in this condition, the discharge pressure Pdincreases to an abnormally high pressure such that a differentialpressure between the discharge pressure Pd and the pressure Pc in thecrankcase exceeds a predetermined pressure (for example, 10 MPa), and aforce pushing the shaft 18 in the valve-opening direction becomeslarger. Thereby the shaft 18 moves in the valve-opening direction whilecompressing the spring 20, with the result that the control valve forvariable displacement compressor is in open state.

In short, in the control valve for variable displacement compressor,when the discharge pressure Pd in the variable displacement compressorabnormally increases, the shaft 18 senses it and moves in thevalve-opening direction, so that the high pressure flows out to thecrankcase. Thereby, the variable displacement compressor shifts tooperate at the minimum discharge capacity, which decreases the dischargepressure Pd, thus making it possible to prevent breakdown caused by theabnormally high pressure.

The above embodiment shows an example where the shaft 18 is looselyfitted in the stationary core 14 and the movable core 16 in a manneraxially extending therethrough. It is preferable that bearings aredisposed in the vicinity of both ends of the shaft 18 for positioningthe shaft 18 on the same axis as the port 11 and the stationary core 14.

A control valve for variable displacement compressor of the presentinvention opens a valve section by a differential pressure between adischarge pressure and a pressure to be introduced into a crankcase whenthe discharge pressure increases to an abnormally high pressure.Therefore, the high pressure flows out to the crankcase, which shiftsthe variable displacement compressor to operate at a minimum dischargecapacity and decreases the abnormally high pressure. As a result, atleast the variable displacement compressor can be prevented from beingbroken due to the abnormally high pressure, which is an advantage.

The foregoing is considered as illustrative only of the principles ofthe present invention. Further, since numerous modifications and changeswill readily occur to those skilled in the art, it is not desired tolimit the invention to the exact construction and applications shown anddescribed, and accordingly, all suitable modifications and equivalentsmay be regarded as falling within the scope of the invention in theappended claims and their equivalents.

1. A control valve for variable displacement compressor for changing adischarge capacity by controlling a flow rate of refrigerant to beintroduced from a discharge chamber to a crankcase of the variabledisplacement compressor with ON/OFF control, the control valvecomprising: a valve section where a valve element is arranged on adownstream side of a valve hole for opening and closing the valve holeinto which the refrigerant that is discharged from the discharge chamberis introduced; and a solenoid for opening the valve section in adeenergized state and for closing the valve section in an energizedstate, wherein, in the solenoid, the valve element is held at avalve-opening position by a first spring imposing an urging force in avalve-opening direction in the deenergized state and a second springimposing an urging force in a valve-closing direction, and is held at avalve-closing position by the second spring in the energized state, thevalve element receiving a discharge pressure of the refrigerantintroduced from the discharge chamber in the valve-opening direction. 2.The control valve for variable displacement compressor according toclaim 1, wherein, in the solenoid, a stroke of a movable core moving tobe attracted by a stationary core in the energized state from a positionwhere the valve element is positioned at the valve-opening position isset longer than a stroke of the valve element moving to thevalve-closing position from the valve-opening position in the energizedstate.
 3. The control valve for variable displacement compressoraccording to claim 2, wherein, in the solenoid, the stationary core, thefirst spring, the movable core, a stopper, and the second spring arearranged from a side of the valve section in this order on a same axisas the valve hole, and a shaft that is loosely fitted in the stationarycore and the movable core in a manner axially extending therethrough hasone end serving as the valve element for opening and closing the valvehole and another end fixed to the stopper.